1. Field of the Invention
The present invention relates to a process for the production of alumina spheres, and, more especially, relates to the production of such spherical shaped articles from an alumina sol via a "sol/gel" process. The invention also relates to the use, e.g., as catalyst or catalyst carrier/support, of the resultant shaped articles.
2. Description of the Prior Art
It is known to this art to prepare spheroidal alumina particles from an alumina sol by the so-called "sol/gel" process, by dripping droplets of the alumina sol into mixtures comprising alumina in a water immiscible liquid, and thence gelling the spheres thus formed.
Thus, the U.S. Pat. No. 2,610,314 [hereby expressly incorporated by reference] describes a process consisting essentially of mixing solutions of an alumina sol and hexamethylenetramine; dispersing the mixture in the form of droplets into a water immiscible forming liquid; and therein aging the spherical shaped articles autogenously formed, at a temperature of 50.degree. to 105.degree. C. and under atmospheric pressure. The resulting spheres are thence subjected to a supplementary aging treatment in an ammoniacal medium and finally are washed, dried and calcined. This process displays the disadvantages of requiring very long aging periods and of necessitating high consumption of ammonia, particularly for the production of low density spheres. In addition, for a given density, the mechanical properties of the spheres are relatively poor.
In order to reduce the aging time required for sphere production, it was proposed, in French Pat. No. 1,172,385 [hereby also expressly incorporated by reference], to perform a single aging treatment in the forming liquid, under pressure and at a temperature in excess of 110.degree. C.; consistent with this particular process, the additional stage of aging in a basic medium is thus entirely eliminated, following the overall aging in the forming liquid. This latter process, though, displays the particular disadvantage of not permitting the ready production of spheres having adequate pore volumes because of the very rapid variation of the pore volume with temperature.